fix: make config file saves atomic

[echobt]

Description

This PR addresses issue #134 regarding non-atomic saves of configuration files. Previously, config files were written directly, which could lead to corruption if the process was interrupted during the write operation.

Changes

• Added uuid dependency to generate unique temporary filenames.
• Implemented write_atomic helper function in a new utils.rs module.
• write_atomic writes content to a temporary file first, then renames it to the target path.
• Updated Config::save in src/config.rs to use write_atomic.
• Updated various config writing operations in src/cli/install.rs to use write_atomic.

Verification

• Added a temporary test suite tests/atomic_write_test.rs to verify the atomic write behavior (creates file, overwrites file, handles directories).
• Ran cargo test successfully.
• Verified that existing tests pass.